Combustion engines such as gas turbine engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor.
A variety of combustor designs exist, with different designs being selected for suitability with a given engine and to achieve desired performance characteristics. One popular combustor design includes a centralized pilot burner (hereinafter referred to as a pilot burner or simply pilot) and several main fuel/air mixing apparatuses, generally referred to in the art as injector nozzles, arranged circumferentially around the pilot burner. With this design, a central pilot flame zone and a mixing region are formed. During operation, the pilot burner selectively produces a stable flame that is anchored in the pilot flame zone, while the fuel/air mixing apparatuses produce a mixed stream of fuel and air in the above-referenced mixing region. The stream of mixed fuel and air flows out of the mixing region, past the pilot flame zone, and into a main combustion zone, where additional combustion occurs. Energy released during combustion is captured by the downstream components to produce electricity or otherwise do work.
It is known that high frequency pressure oscillations may be generated from the coupling between heat release from the combustion process and the acoustics of the combustion chamber. If these pressure oscillations, which are sometimes referred to as combustion dynamics, reach a certain amplitude they may cause nearby structures to vibrate and ultimately break. A particularly undesired situation is when a combustion-generated acoustic wave has a frequency at or near the natural frequency of a component of the gas turbine engine. Such adverse synchronicity may result in sympathetic vibration and ultimate breakage or other failure of such component Various modifications of and devices for the combustion section of a gas turbine engine have been developed to address the problem of combustion-generated acoustic waves. For example, U.S. Pat. No. 6,164,058 issued Dec. 26, 2000, to Dobbeling et al., teaches a quarter wave resonator extending either into the diffuser or into an annular collecting space about the combustor. U.S. Pat. No. 5,685,157, to Pandalai et al., also teaches a quarter wave resonator, however here a plurality of closed-end resonators are provided circumferentially around the burners of the engine.
Other approaches to damp undesired acoustic vibration utilize a Helmholtz resonator. A plurality of such resonators may be placed along the outside surface of the combustion chamber or the transition downstream of the combustion chamber. The latter is done for example, in U.S. Pat. No. 6,530,221, issued Mar. 11, 2003, to Sattinger et al. The Sattinger et al. patent teaches the placement of damping modular resonators at locations having the highest acoustic pressure amplitude, which for a particular gas turbine engine was identified to be at two locations in the transition. This patent also teaches the positioning of modular resonators disposed in the flow path in positions adjacent to tubular members that house combustor elements. U.S. Pat. No. 6,640,544, issued Nov. 4, 2003, to Suenage et al., and U.S. Pat. No. 6,837,051, issued Jan. 4, 2005, to Mandai et al., teach aspects of resonators positioned along the outer wall structure of combustion chambers.
It is recognized that a fixed volume resonator may damp vibrations only within a defined range of frequencies based upon its volume and aspects of the opening leading into it from the source of vibrations. To address this issue, U.S. Pat. No. 6,634,457, issued Oct. 21, 2003 to Paschereit et al., teaches a device for damping combustor acoustic vibrations in which the volume of a Helmholtz resonator can be changed by adding or draining a fluid via a supply line, or by other means.
U.S. Pat. No. 5,644,918, issued Jul. 8, 1997 to Gulati et al., teaches the installation of Helmholtz resonators in two relatively upstream locations. One or more “head end” resonators may be placed adjacent and lateral to the fuel nozzle assemblies in the combustor area. Tubes extend from the combustion chamber into respective the cavities of the respective “head end” resonators, which are within a main axial flow path of air entering for combustion. The “side-mounted” resonators are spaced apart from the combustion chamber, and are positioned circumferentially in a space through which compressed air passes as it flows into the combustor. Tubes extend through that space from the combustion chamber to communicate with the cavities of such “side-mounted” resonators.
Also, a Helmholtz resonator for an annular combustor of a gas turbine engine is taught in US patent publication number US2005/0144950 A1, published Jul. 7, 2005, having inventors Flohr et al. The Helmholtz resonator is integrated into a combustor insert, which is located between a combustor and a combustion chamber. Small tubes provide fluid communication between an upstream end of the combustion chamber and the resonator, and the latter also is shown to comprise air inlets.
While the above approaches may provide one or more favorable features, there still remains in the art a need for a more effective and efficient resonator, and for a gas turbine engine comprising such resonator, to address undesired combustion-generated acoustic waves.